Because it shows many people are playing it. That in itself may be of interest to people who are considering purchasing the game. Also it let’s the devs know there is a market potentially interested in DLC or sequels. If the news was that player counts dropped to a very small number, neither of those things are likely to happen
Your UI looks like you’re using iOS. In the app store, at the bottom of the page for each app is a list of items available for purchase in the app. You can look at that list before even deciding to download anything. Sometimes the listing’s are vague and just say something like “membership”. In that case, for a language learning app, you can assume it is to unlock “certificates”.